Hydraulic brake master cylinder reservoir float switch



Oct. 21, 1952 D. M. WHITNEY HYDRAULIC BRAKE MASTER CYLINDER RESERVOIR FLOAT SWITCH Filed Feb. 2l, 1949 6 fb I/ i 15 L u y 3 y A f W. l; y h

Patented Oct. 21, 1952 HYDRAULIC BRAKE MASTER CYLINDER RESERVOIR FLOAT SWITCH David M. Whitney, Toledo, Ohio Application February 21, 1949, serial No. 77,602

3 Claims.

This invention relates to signalling critical subsidence in power liquid control system, primarily from manual direction of the liquid in the system, with automatic independent actuation of the signal bythe liquid.

This invention has utility when incorporated as a readily substitutive accessory for the lling plug at the master cylinder in a hydraulic brake system, say of the four wheel type for motor vehicles. Normally the master cylinder is provided with a power fluid reserve reservoir thereover,"coacting as a replenishing means for the system'. Besides oozing back and forth between the master cylinder and the reserve chainber therefor to cause the liquid level in the reservoir to change in the normal operation, there is in addition thereto, considerable disturbance for'the less than full reservoir due to vehicle travel, stopping and starting. In place of the vented refilling plug or closure for the reservoir, there is herein provided an electric switch, or check, with its operating means of float type, shielded from vehicle lunges, and providing a stable control coacting at lowered power liquid level toward depletion of the reserve, to give a signal, say a light at the dash, so that the driver of the `car is warned timely as to brake operation impending failure.

Referring to the drawings:

Fig. 1 is a side elevation of a master cylinder and brake pedal operator therefor, with wiring fora signal circuit, and dotted line showing of the four wheel brake ducts for the hydraulic brake system;

Fig. 2 is an enlarged View, with parts broken away of the master cylinder of Fig. 1, in switch closing position; and

Fig. 3 is a vertical section, on a somewhat larger scale of the accessory switch providing plug terminal at open position for the switch.

A motor vehicle I is provided with a brake pedal 2 having a iixed fulcrum 3. From the pedal 2 and xed therewith is a short arm 4 beyond the fulcrum 3. The arm 4 is pivotally connected to a piston rod 5 extending into a trunk piston having a forward packed end 6 and a follower packed end I with a. tapered connecting portion 8 having va chamber 9 thereabout between the piston end portions 6, 'I.

The piston 6, 1, is slidable in a cylinder I0 having an open or discharge end I I remote from the piston 6, 1. A seat I2 in the cylinder I0 adjacent the open end II, is engaged by a helical compression spring I3 extending to the piston 6, "I, and rrnly holding the piston 6, 'I, against the plunger type of piston rod 5.

A housing I4 for the cylinder I0 has an upward extension providing a chamber or reservoir I5 for a reserve supply I6 of power liquid for the hydraulic brake system. At non-depressed position for the brake pedal 2, the piston end 6 leaves a port II in the bottom of the reservoir I5 incommunication with the chamber 9. A somewhat smaller, seepage or by-pass port I8 connects Vthe bottom of the reservoir I5 with a chamber I9 in which is located the spring I3.

The driver of the vehicle I, as'occasion arises for applying brakes or stopping the automobile, may use his foot to depress the pedal 2. The spring I3 is compressed, and the piston end 6 rides along in the chamber I9 of the cylinder I0 past the port I8. The power liquid in the chamber I9, as fully'charged, is thereby forced therefrom thru the end II by duct 20 and thru branches 2l, 22, to hydraulic brake cylinders at rear wheels 23, 24. In parallel with the duct 20 from the end II, is a duct 25 extending forwardly to branches 26, 21, connected respectively to hydraulic brake cylinders in forward vehicle wheels 28, 29. The reservoir I5 has an internallythreaded, charging or refilling opening 30 in its top for replenishing power liquid supply.

Under the invention herein, an automatic electric `switch or float-controlled contact is adopted instead of a normal closure plug at the replenishing opening 33. To this end there is provided a hollow plug or reducing bushing 3l. Brazed or welded thereto is a concentric sleeve or extension 32 having a lower open end 33 bounded by a slight inward flange 34 sufficient to preclude" annular clearance 39 relative to the inside of the sleeve 32. Outward from the chamber I5, there is a small vent opening 40past the insulation 36 and thru the plug 3l. Supplemental thereto, there is a port 4I of sufficiently small diameter to allow a relatively slow rate of liquid outflow from within the sleeve 32, as in operation such excess may be lodged above the float 35 y(or pumped thereto by way of the clearance 39. This means that there may Iarise dashpct operation from sudden changes in liquid level in the reservoir I5, and that it establishes no quick throws or spasmodic operations, but the iioat has a retarded or stable functioning. It follows that from this effective control, so long as the mean liquid level upper surface for the power liquid I6 in the reservoir sunciently sustains the float 35 that contact end 4I for the guide 38 is away from bottom wall 42 of the reservoir I5, this automatic switch is open. In normal practice, thrusting of the pedal 2 to eifect application of the brakes at the wheels 23, 24, 28, 29, may give an oscillation disturbance of as much as The electric circuit The contact rod 31 has a terminal or head 43 upward from the insulation 38. To this may be attached a spark-plug type of clip with a conductor line 44 to a signal, herein shown as a light 45, readily visible to the vehicle driver, say for such to be located on or adjacent to the instrument panel or dash region.

From the visible signal 45 a line 46 extends to the ignition switch III. By this provision, at any condition of power iiuid depletion, before replenishment has occurred, the standing car at out-of-service condition, is not experiencing running down of its battery, for at such times the ignition switch Il is normally open. The circuit from the ignition switch 4I is by a line 48 to a battery 49 having a ground 5G, common to the ground i2 as the bottom wall of the power fluid carrying chamber I5, or even a contact in the sleeve.

In operation of the vehicle, there is normally considerable swishing of the upper surface of the power liquid l in the reservoir I5. This somewhat wide range in the top surface condition for the power liquid, is materially stabilized before effective to disturb the automatic switch, which has its float shielded by the sleeve 32. Furthermore, any bobbing freely of the float 35 does not take place, for above the float 35 is a dashpot chamber 5I. The small cross-section of the vent duct Iii) is primarily to allow suflicient air to enter the chamber I5 above the level of the power liquid I5 so that in the normal brake operation as eiiected from the pedal 2, the power liquid is released for entrance to the chambers '3, I9, by the ports Il, I8, to keep the master cylinder Il replenished. Also, with the vent d from the chamber I5, there may be backfiow into the chamber I5, say as there may be excess flow to the cylinder I0, or to compensate for fluid expansion from temperature change or rise. or above the oat 35 coacts as a dashpot in its iiow, with possibly some air thru the port 4I, which also may relieve the chamber 5I from holding the float 35 from properly settling to the actual liquid telltale therefor.

Normally with the motor vehicle idle and accordingly not set for the internal combustion engine or motor to function, the iirst action to be taken by the chauffeur or driver is to cut in the ignition switch EII so that the motor may operate. The brake pedal 2 is at released position. From driving there is stopping or vehicle holding from rolling, eifected by the operation of the brake pedal 2 to shift the piston 6, 1, in

the master cylinder ID. The inward travel of the piston rod 5 as to the cylinder I0 delivers uid pressure thru the ducts 2), 25, to the respective brake band controls at the several wheels of the vehicle. There are various joints thruout the system, as well as for thepiston 6, '1, as to the More sluggish than air, liquid as pumped cylinder II). The dissipation of the control volume for the liquid is almost negligible with the installation in good order. However, there is always some depletion and as such reserve volume becomes so low in the reservoir I5 that there is not replenisment excess for the cylinder I0, there is hazard or" possible defective brake functioning in a stop emergency, Under the invention herein, as the reservoir I5 is not quite exhausted of reserve liquid, the low level of such liquid I6 is not suflicient to hold the float 35 poised and it settles down for its sleeve 4I to strike the top side of the cylinder IU for a. ground 42 in completing a circuit now past the closed ignition switch l, thru the line 46, the signal 43, the line 44, to the rod 43, the guide 48, now performing as an automatic switch in contacting the ground 42, the ground 50, the energy source 9, and the line 48 to the opposite side of the switch 41. It is thus seen that the automatic signal circuit is only in during the ignition circuit being on and in parallel therewith to a common ground. Upon replenishing liquid in the chamber I5 by removing the plug 3| and thereafter replacing the plug, there is now sucient liquid in the reservoir I5 to keep the float 35 poised during the operation of the piston in the cylinder IU.

What is claimed and it is desired to secure by Letters Patent is:

i. A brake iluid level warning device adapted for attachment to a master cylinder reservoir and functioning to operate an electrical signal on a vehicle, said device comprising a hollow plug having an externally threaded portion for screwing said threaded portion into and out of the reservoir, a cylindrical iioat operable by change of level of the fluid in the reservoir, there being a cylindrical guide in which the float opcrates, said cylindrical guide extending downwardly from said plug into the reservoir and normally into the uid to coact with said float to retard its operation, an electrically conducting guide rod axial of said plug extending above said plug to an electrical terminal and extending into the reservoir short of the extension of sai-d cylindrical guide, an electrical insulation ring supporting said guide rod in said plug and closing the hollow space in said plug, electrical conducting means xed with and vertically extending away from said iioat, adapted for closing a circuit with said guide rod when said float is at a critical level for the fluid in the reservoir.

2. In a brake fluid level warning device for an electrical-ignition-equipped vehicle having in a series circuit a signal and an ignition switch, said device being adapted for attachment to a master cylinder reservoir in pla-ce of the lling plug for said reservoir, said device including a cylinder mountable to extend downwardly into the reservoir which reservoir coacts for one side of an electrical circuit, an insulation ller providing a closure for the top end of the cylinder, a contact rod mounted in the filler to be thereby insulated from the reservoir, said rod extending downwardly from the filler into the cylinder, and a iioat in the cylinder, said float having guide means adapted to slidably coact between the Iloat and rod in directing up and down shifting of the float in the cylinder relatively to the rod, said guide means at a down limit of the iioat shifting having a portion coacting between the rod and reservoir to form a closed switch to bypass the insulation ller.

3. In a brake iiuid level warning self-contained-dashpot device for an electrical-ignitionequipped vehicle having in a series circuit a, signal and an ignition switch, said device being adapted as assembled therewith to coact as a filler plug for a master cylinder reservoir, said device including a dashpot cylinder mountable to extend downwardly into the reservoir, which reservoir coacts for one side of an electrical circuit, an insulation'ller providing a closure for the top end of the cylinder, a contact rod mounted in the filler and thereby insulated from the reservoir, said rod extending downwardly from the filler into the cylinder, a dashpot piston float in the cylinder, said float having guide means adapted to shiftably coact between the float .and rod in directing up and down movement of the float in the cylinder relatively to the rod, there being dashpot operation dampening means including a vent from the cylinder at the filler, at a down limit position for the float said guide means having :a portion coacting between the rod and reservoir to form a closed switch to bypass the insulation filler. i

DAVID M. WHITNEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,161,441 Vickers June 6, 1939 2,253,260 Alcorn Aug. 19, 1941 2,479,503 Moore Aug. 16, 1949 2,494,802 Fox Jan. 17, 1950 

